During some conditions, turbocharged direct-injection engines may generate increased soot. For example, during some conditions, fuel may not sufficiently mix with air before combustion, for example due to reduced turbulence. Such phenomena may occur when the engine is operating at high speed and/or high loads.
The inventors herein have recognized that one approach to address such an issue may be to utilize a particulate filter in the exhaust. However, regeneration of the filter in the exhaust of a spark-ignited engine aimed at stoichoimetric emission control raises numerous issues. As just an example, sufficient excess oxygen for regeneration in the exhaust may result in increased NOx emissions.
Systems and methods for controlling regeneration of a particulate filter downstream of an engine having a plurality of cylinders are provided herein. One exemplary method includes, during first conditions, spinning down the engine to non-combusting engine rest, and regenerating the particulate filter at least during engine rest. The method also includes, during second conditions, regenerating the particulate filter during combustion of at least one cylinder of the engine.
By regenerating the particulate filter during engine shutdown and/or engine rest in some conditions, it is possible to reduce engine running regeneration, which can thereby lead to reduced engine running emissions. For example, if engine running regeneration utilizes excessive lean operation, thus increasing NOx emissions, reducing the amount of engine running regeneration in favor of shutdown regeneration can therefore reduce engine running NOx emissions. Further, excess oxygen in the exhaust during engine shutdown may interfere less with NOx conversion since non-combusting operation results in significantly less, and possibly no, engine out NOx.
Finally, by regenerating the particulate filter during engine combustion in some conditions, and during engine rest in other conditions, particulate filter regeneration can be carried out with more flexibility. As one example, regeneration during engine combustion may be carried out when there is more particulate stored at the particulate filter compared to a time when regeneration during engine shutdown and/or engine rest is carried out. As another example, it may be desirable to regenerate a particulate filter before a time for engine shutdown is reached. In such a situation, regeneration during engine combusting may be carried out, and then carried through to engine rest conditions.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.